Users running Windows XP, Windows Vista or Windows 7 will be able to download an upgrade to their OS to Windows 8 Pro for $39.99 in 131 markets once the new Windows OS version becomes available, Microsoft announced on Monday.

Users running Windows XP, Windows Vista or Windows 7 will be able to download an upgrade to their OS to Windows 8 Pro for US$39.99 in 131 markets once the new Windows OS version becomes available, Microsoft announced on Monday.

The company hasn't given an official date for the commercial availability of Windows 8, but it's widely assumed that it will ship before the end of the year. The offer includes a free option to add Windows Media Center.

Among the elements this upgrade assistant checks is whether the user's PC needs any tweaks or changes to support Windows 8 Pro.

"It will also inform you of any application or device compatibility issues," the blog post reads.

Depending from which OS they're upgrading, users will be able to transfer different components to Windows 8 Pro. Those on any Windows 7 consumer edition will be able to migrate their Windows settings, personal files and applications. People upgrading from Windows Vista will be able to carry over their Windows settings and personal files. Windows XP users will only be able to bring along their personal files.

"Of course, if you want to start fresh, you can choose to bring nothing along. Or if you prefer to format your hard drive as part of your upgrade experience, you can do so as long as you boot from media and then format your hard drive from within the setup experience for installing Windows 8, not prior to it," the blog post reads.

Users who prefer to buy a shrink-wrapped Windows 8 upgrade DVD at a retail store can do so for US$69.99.

These are special prices both for the download and the DVD options. The offer ends on Jan. 31, 2013.

A few weeks ago, Microsoft announced a different Windows 8 upgrade offer for consumers who buy new Windows 7 PCs between June 2 and Jan. 31, 2013. Those users will be able to upgrade to Windows 8 Pro for $14.99. This Windows Upgrade Offer is available in 131 markets.

Microsoft hasn't disclosed retail prices for shrink-wrapped, stand-alone versions of Windows 8, but the equivalent to Windows 8 Pro is Windows 7 Professional, which is priced at $199.99. Windows 7 editions that qualify for that offer are Home Basic, Home Premium, Professional and Ultimate. That leaves out of this offer's scope Windows 7 Starter, which is the most basic for consumers, and Windows 7 Enterprise, which is designed for workplace PCs.

An interesting wrinkle in that offer for buyers of new Windows 7 PCs is that they don't need to apply the Windows 8 upgrade to the corresponding Windows 7 PC they bought during the offer period. If they have an older PC running, for example, Windows XP, they can opt to leave Windows 7 on the new PC and upgrade the old one to Windows 8 using the upgrade download.